Breakdown processes in gas micro-bubbles in liquids under electric stress

The present work is concerned with a theoretical analysis of the breakdown characteristics of gas-filled micro-bubbles formed in insulating liquids stressed with electric field. It is assumed that the gas inside these bubbles is air which allows the use of experimental Paschen curve data for air in this analysis. Two main discharge mechanisms have been considered, the Townsend discharge and impulse breakdown. The combination of bubble diameter, D, gas pressure, p, and duration, τ, of the field stress determines the type of breakdown. Parameters which are required for the Townsend mechanism of breakdown and impulse breakdown to occur inside gas bubbles have been obtained and these conditions have been represented as boundary lines in the (Dp, τp) coordinate system. It is shown that there are such combinations of these parameters which satisfy neither Townsend nor impulse breakdown conditions. Experimental data on breakdown in air for these intermediate values of (Dp, tp) between the Townsend and the impulse discharges are not available in the literature and the breakdown behavior under such conditions is not well defined.